Conventional automotive vehicles include a powertrain (sometimes referred to as “drivetrain”) that is generally comprised of an engine in power flow communication with a final drive system (e.g., differential and wheels) via a multi-speed power transmission. Automobiles have traditionally been powered solely by a compression-ignited or spark-ignited internal combustion engine (ICE) because of its ready availability and relative cost. Hybrid type powertrains, on the other hand, generally employ one or more motor/generator units that operate individually or in concert with an internal combustion engine to propel the vehicle.
One premise behind hybrid-type vehicles is that alternative power is available to propel the vehicle, minimizing reliance on the engine for power, thereby increasing fuel economy. The hybrid powertrain takes advantage of both the ICE and motor/generator(s) to improve upon fuel economy and exhaust emissions. Since hybrid-type vehicles can derive their power from sources other than the engine, engines in hybrid-type vehicles typically operate at lower speeds more often than their traditional counterpart, and can be turned off while the vehicle is propelled by the alternative power source(s). Moreover, many hybrid vehicles use electrical regenerative braking to recharge an internal electrical power storage device.
Electric vehicles (EV) and hybrid electric vehicles (HEV) use battery packs, often comprised of several individual battery modules, to provide current to the motor/generators in order to propel the vehicle and operate vehicle accessories. It is well known that excessively hot temperatures may degrade overall battery performance and reduce battery operational life expectancy. For HEVs, hot temperatures can limit hybrid system performance, which can mean inconsistent operation and lower fuel economy. In addition, hybrid-electric vehicle batteries are generally larger and more complex than traditional Starting-Lighting-and-Ignition (SLI) batteries; thus, replacing HEV battery modules is costly.
When an automobile, hybrid or otherwise, is parked with the windows closed on a sunny day, the solar load can quickly heat both the passenger and trunk compartments well beyond the outside ambient temperature. On a typical 80 degrees Fahrenheit (° F.) sunny day, for example, inside vehicle temperatures can exceed 115° F. With a vehicle soaking in these conditions for a prolonged period of time, an operator that enters the vehicle may experience unbearably hot temperatures upon entering the vehicle. If full hybrid performance were then to be allowed, the batteries would heat even more under normal use, and reduced battery life would result. If hybrid battery usage was limited to protect battery life, hybrid performance would suffer.